The invention pertains to a roofing system in which the roof is overlayed with sheet rubber and secured in place by a plurality of spaced apart holddowns and more particularly to improvements in the system, the method of securing the sheet rubber in place and the holddown.
For some years, it has been common practice to cover roofs that extend horizontally or at comparitively small angles of inclination with sheets of rubber. Such a roof is good protection against the penetration of water to the framework of the roof and is more durable than conventional BUR roofing of tar and tar paper. The term "rubber" in this application is used to encompass polyvinyl chloride sheets, EPDM sheets, and other natural or synthetic resinous materials having the physical and chemical properties of a "rubber". These rubber sheets are usually laid on top of a neat insulating under layer and naturally must be anchored so as not to be blown off or slide away from the roof. For this purpose, in the past, the rubber sheets are, for the most part, adhesively secured to the under layer or overlaid with gravel. In one type of installation the sheets are secured by means of spaced apart holddowns in the form of plates or moldings of sheet metal or plastic through which are passed fasteners, such as screws or nails, which are in turn screwed or nailed into the roof support. Such a prior art roofing system is disclosed in U.S. Pat. No. 4,074,501 issued to Sandqvist on Feb. 21, 1978.
Holddowns, washers or other devices used in conjunction with a fastener are very old. They act by spreading the force applied by the fastener over a larger area than that of the head of the fastener. This reduces stress at any one point and helps secure the fastened item. The shortcoming of these holddowns is that their useful size is limited since they do not apply force well over an area much in excess of the size of the head of the fastener. This limits their usefulness in situations where large stresses are applied to a relatively fragile material such as in securing roof system membranes. Additionally, these holddowns may damage the rubber sheets upon installation and because of such damage or other reasons do not provide a good watertight seal even when used in conjunction with caulking or rubber members in applications where stresses are large such as in roof system membranes.
It is therefore highly desirable to provide an improved holddown and roofing system and method. The holddown comprises a body encasing a deformable spring. The body being deformable from an unconstrained shape to a constrained shape by application of a compressive force by displacement of a fastener interpositioned within a hole in the body of the holddown.
It is also highly desirable to provide an improved holddown that applies a force over a large area.
It is further highly desirable to provide an improved holddown and roofing system and method that can be used with a fastener and pliant filler to affix material in watertight relationship to a structure.
It is likewise highly desirable to provide an mproved holddown that provides a tight seal when it is attached.
It is yet also highly desirable to provide an improved holddown and roofing system and method that is easy and economical to use.
It is still further highly desirable to provide an improved holddown that when used on top of a membrane in a roof system can withstand wind uplift.
It is yet further highly desirable to provide an improved holddown that has a smoothly tapered upper surface that will not trip persons walking over it.
It would finally be highly desirable to provide an improved holddown which meets all the above desired features.